Editing Menstrual cycle (section)

==== Proliferative phase ====
[[File:Estradiol and progesterone % changes across the menstrual cycle.tif|thumb|upright=1.6|During the menstrual cycle, levels of estradiol (an estrogen) vary by 200 percent. Levels of progesterone vary by over 1200 percent.<ref>{{cite journal|vauthors=Prior JC|title=Women's reproductive system as balanced estradiol and progesterone actions—A revolutionary, paradigm-shifting concept in women's health|journal=Drug Discovery Today: Disease Models|volume=32 | issue = Part B|year=2020|pages=31–40|doi=10.1016/j.ddmod.2020.11.005|ref=none|doi-access=free}}</ref>]]

The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow and proliferate.{{sfn | Ugwumadu | 2014 | p= 117}} The latter part of the follicular phase overlaps with the proliferative phase of the uterine cycle.{{sfn|Parker|2019|p=283}} As they mature, the ovarian follicles secrete increasing amounts of [[estradiol]], an estrogen. The estrogens initiate the formation of a new layer of endometrium in the uterus with the spiral arterioles.{{sfn|Tortora|2017|p=944}}

As estrogen levels increase, cells in the cervix produce a type of [[cervical mucus]]<ref>{{cite journal |vauthors=Simmons RG, Jennings V |title=Fertility awareness-based methods of family planning |journal=Best Practice & Research. Clinical Obstetrics & Gynaecology |volume=66 |pages=68–82 |date=July 2020 |pmid=32169418 |doi=10.1016/j.bpobgyn.2019.12.003 |doi-access=free |type= Review}}</ref> that has a higher [[pH]] and is less [[viscosity|viscous]] than usual, rendering it more friendly to sperm.{{sfn|Tortora|2017|pp=936–937}} This increases the chances of fertilization, which occurs around day 11 to day 14.{{sfn|Tortora|2017|p=957}} This cervical mucus can be detected as a vaginal discharge that is copious and resembles raw egg whites.<ref name= Su2017 /> For women who are practicing [[fertility awareness]], it is a sign that ovulation may be about to take place,<ref name= Su2017>{{cite journal |vauthors=Su HW, Yi YC, Wei TY, Chang TC, Cheng CM |title=Detection of ovulation, a review of currently available methods |journal=Bioeng Transl Med |volume=2 |issue=3 |pages=238–246 |date=September 2017 |pmid=29313033 |pmc=5689497 |doi=10.1002/btm2.10058 |type= Review}}</ref> but it does not mean ovulation will definitely occur.{{sfn|Prior|2020|p=45}}